This research will examine how "molecular" (small-scale) variables affect choice behavior. One major variable to be investigated will be delay of reinforcement, and its role in "self-control" choices (where a subject must choose between a small, immediate reinforcer and a larger but delayed reinforcer). Choice behavior will also be studied in situations where the alternatives include one certain reinforcer and one probabilistic reinforcer. The subjects in this research will be pigeons performing in standard operant conditioning chambers, and two main procedures will be used to study their choice behavior. One is an adjusting-delay procedure developed by the PI, in which the delay for one alternative is systematically increased and decreased over trials in order to find a delay at which the subject chooses both alternatives equally often. The second procedure is also a discrete-trials procedure, but one in which each of two response keys has a specified probability of reinforcement. The purpose of this procedure is to observe the acquisition of choice behavior when one alternative has a higher probability of reinforcement than the other. Some of the proposed experiments are designed to distinguish between the PI's theory and other theories about delay and probability of reinforcement. Other studies will test some current theories about the acquisition of preference in choice situations. The proposed experiments should help to decide which of these different theories are viable and which are not. Many important everyday choices involve a conflict between an individual's short-term and long-term interests (e.g., the pleasures of smoking, drinking, or overeating versus future health). In addition, many everyday decisions must be made when the consequences of one's actions are by no means certain. For these reasons, it seems appropriate to submit this proposal, which will investigate the effects of delayed and uncertain reinforcers, to NIMH.